The following relates generally to the optical components used in optical communication networks, and specifically to optical devices that can filter optical signals, while providing the functions of wavelength tuning, as well as power isolation of the optical signal.
Erbium-Doped Fiber Amplifiers (EDFAs) or Praseodymium-doped fiber Amplifiers (PDFAs) are widely deployed in optical networks, in the 1550 nm or 1310 nm wavelength windows, respectively. FIG. 1 illustrates the optical components that are typically included in a prior art EDFA. Note that PDFAs use a similar configuration. The optical power from the pump light source 102 boosts the Erbium ions embedded in the erbium-doped fiber 103 to a higher energy level. The optical input signal 101 then induces stimulated emission and is therefore amplified to create the output signal. However, amplified spontaneous emission (ASE) noise is also generated simultaneously, and creates noise on top of the input signal 101. Thus the output signal 111 consists of an amplified input signal, as well as the ASE noise component. Two isolators, 109 and 110, are located on the input side of a WDM coupler 107, and after the erbium-doped fiber 103, respectively. The second isolator B (110) is intended to prevent the back scattering power out of the downstream optical fiber and other components from re-entering the EDFA. This unwanted back scattering power would otherwise be amplified, and would therefore interfere with the EDFA's normal characteristics and performance. The first isolator A (109) is intended to block the ASE noise and back scattering that are generated inside the EDFA, from propagating upstream and interfering with the input signal 101.
An optical filter 112 is also used to filter out most of the unwanted ASE noise that exits the output signal port 111, so that only the intended optical signal wavelength or bandwidth is allowed to pass through the filter. In today's advanced, re-configurable optical networks, the signal wavelength can be dynamically changed to provide flexibility in the overall network configuration. Therefore, a tunable optical filter 112 is typically used, and must be tuned or adjusted so that its passband matches the wavelength change in input signal 101.
As has been occurring with cell phones, more and more components are being squeezed into individual optical modules, with the same limited volume, in order to save space, and also to upgrade the performance of network control centers. Fiber splicing between separate fiber optic components is cumbersome, and also occupies space. It is therefore desirable to integrate multiple optical components into a single package. In the case of EDFAs, as illustrated in FIG. 1, it is desirable for the optical tunable filter 112 to be physically integrated with isolator B (110).